1) Field of the Invention
The present invention concerns polyester fabric that is employed in airbags. In particular, the polyester fabric has improved resistance to edge combing—the relative tendency of a fabric to pull apart under seam stress or similar action such as inflation of inflatable restraints. Further, the polyester fabric of the invention must have an edge comb resistance of greater than about 350 Newtons at room temperature (20° C.) and greater than 250 Newtons at 90° C. The polyester fabric of the invention has an acrylic polymer, copolymer, or polymer blend finish applied from about 1 to about 4 wt. % nominal solids add-on of said fabric.
2) Prior Art
Conventional air bags are produced by coating or laminating a plain weave fabric with an elastomer resin such as a synthetic rubber, for example chloroprene, chlorosulfonated olefin or silicone, to provide a base fabric with low air permeability, and cutting and sewing the base fabric into bags. The elastomer resin is applied to the surface of the base fabric in an amount of 90 to 120 g/m2, and the air bag produced is very heavy, hard and coarse in appearance. Furthermore, when it is folded into a compact module, it is hard to fold. If the base fabric is coated with silicone elastomer resin, the air bag is considerably more heat resistant and cold resistant than an air bag having a base fabric coated with chloroprene elastomer resin. Moreover, the amount of resin coated is only 40 to 60 g/m2, thus allowing a reduction in weight and an improvement in appearance and foldability.
U.S. Pat. Nos. 6,545,092, 6,348,543 and 6,468,929 to Parker discloses a coating to improve edge comb resistance. This coating is a cross-linked blend of polyalkyl/polyphenoxy siloxane with a copolymer of ethylene and methacrylate.
U.S. Pat. No. 3,705,645 to Konen discloses an acrylic polymer coating as a film laminate on the inside of the airbag.
U.S. Pat. No. 5,800,883 to Koseki discloses a polyurethane resin coated airbag.
Many others used silicone resin coatings that also created a film on top of the fibers thereby creating an air impermeable airbag. These airbags exhibit reduced seam combing. It is also known to use a silicone/urethane or silicone/acrylic copolymer coating to improve tear strength.
U.S. Pat. No. 6,169,043 to Li discloses an airbag coated with polyacrylate and polyurethane copolymer resin to reduce air permeability. No mention is made of seam or edge combing. This patent shows that polyacrylate by itself is inferior to polyacrylate and polyurethane copolymer resin with respect to air permeability.
U.S. Pat. No. 6,291,040 to Moriwaki et al discloses a nylon airbag fabric thinly coated with an thermoplastic synthetic resin, preferably a polyurethane or polyester based resin to prevent edge combing by bridging the interstices of the fabric with the resin.
However, as yet, such improvement is not regarded as sufficient. The coating must withstand extreme conditions in the folded state. For instance the coating must not crack or become sticky, and the airbag must deploy without seam combing (the relative tendency of a fabric to pull apart under stress, due to inflation, at the seams) after prolonged storage at −40° C., and at 90° C.
In addition, it is also demanded that the base fabric for air bags be less expensive and more easily folded for reducing the size of the module. Thus, air bags using non-coated base fabrics have attracted attention. However, they become frayed during sewing and exhibit seam combing.
Uncoated nylon fabrics for airbags have edge comb resistance that are superior to polyester fabric used for the same purpose. To make polyester airbags competitive with nylon airbags, it is desirable to increase the edge comb resistance of polyester fabrics used in airbags. There is therefore a need for an uncoated polyester air bag that exhibits equivalent or superior edge comb resistance at ambient and high temperatures.